Exhaust diffuser for a truck

ABSTRACT

An exhaust diluting and diffusing apparatus includes a first pipe forming a vertically directed outlet for an exhaust conduit and a second diffuser pipe mounted to receive an exhaust gas flow from the outlet of the first pipe, the second pipe having a diameter greater than the diameter of the first pipe to define an ambient air inlet gap surrounding the outlet of the first pipe, and being sufficiently wide to allow the exhaust gas to expand and diffuse in the second pipe. The device further includes a dispersing outlet mounted at an end of the second pipe and configured to direct exhaust gas radially outward, an area defined by the diffuser outlet being greater than an area of the outlet of the first pipe.

The invention relates to devices mounted on truck exhaust systems todilute and diffuse the exhaust gas for release to the environment.

BACKGROUND

Exhaust treatment devices in trucks require maintenance procedures thatcan create situations where exhaust temperatures are much higher thanduring normal use of the vehicle. For example, diesel particulatefilters, which trap soot and other particulate matter in the exhauststream, require a regeneration process to burn off the collectedparticulate matter. The process requires that the temperature of theexhaust entering the diesel particulate filter be in excess of 600° C.Normal operating exhaust temperature is about 425° C. for a dieselengine in a truck.

Exhausting the higher temperature stream to the environment can posedifficulties, particularly for trucks operating in close environments. Atruck typically has an exhaust stack pipe rising from the chassisadjacent to the truck cab. High temperature exhaust can produce a hotspot on the truck cab or trailer, or direct hot gases to a building(such as at a loading dock) or an overhanging tree.

What is needed is a device to reduce the exhaust temperature of aninternal combustion engine.

SUMMARY OF THE INVENTION

The invention includes an exhaust diffuser, a relatively short,relatively wide stack mounted on an exhaust pipe. The diffuser allowsentering exhaust gas and its heat energy to diffuse over the largervolume. The stack induces a buoyancy induced flow that is created by thedifference in density between the low density, high energy exhaust flow,and the higher density of the surrounding ambient air. This buoyancyinduced flow, or “stack effect”, induces a flow of ambient air into theexhaust diffuser, which mixes with hot exhaust gas and cools it.

The invention further includes an outlet formed as axi-symetric louversmounted at the top of the stack. The louvers include a central diverterto balance the flow distribution radially. The outlet louvers define agreater area than the outlet of the exhaust pipe so also to act as adiffuser. This decelerates the exhaust gas flow as it flows from theoutlet which allows it to readily mix with additional ambient air, whichfurther cools the exhaust gas. The combination of the “stack effect” and“diffuser mixing effect” cool the exhaust gas by an amount that neitherwould be able to achieve on their own.

The loss in stack effect due to reduced height is countered by theincreasing the diameter so as to better utilize the flow energy.

An exhaust diluting and diffusing apparatus in accordance with theinvention includes a first pipe forming a vertically directed outlet foran exhaust conduit and a second diffuser pipe mounted to receive anexhaust gas flow from the outlet of the first pipe, the second pipehaving a diameter greater than the diameter of the first pipe to definean ambient air inlet gap surrounding the outlet of the first pipe, andbeing sufficiently wide to allow the exhaust gas to expand and diffusein the second pipe. The device further includes a dispersing outletmounted at an end of the second pipe and configured to direct exhaustgas radially outward, an area defined by the diffuser outlet beinggreater than an area of the outlet of the first pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the followingdetailed description read in conjunction with the appended drawings, inwhich:

FIG. 1 illustrates an embodiment of an exhaust stack dilution anddiffusion element in perspective view;

FIG. 2 is an exploded view of the exhaust stack dilution and diffusionelement of FIG. 1; and,

FIG. 3 is a schematic view of the exhaust stack dilution and diffusionelement of the invention illustrating certain size relationships.

DETAILED DESCRIPTION

The invention relates to devices that are mounted on a truck exhaustsystem at the point where exhaust gas is released to the surroundingair. In particular, the invention is an apparatus mounted on an exhaustconduit downstream of a diesel particulate filter to diffuse the hotgases exiting the diesel particulate filter over a wide area. Accordingto another aspect of the invention, structure is provided to diluteexhaust gases with ambient air and diffuse the diluted exhaust gas overa wider area than a typical exhaust stack pipe to prevent hot spots anddissipate heat more quickly.

FIG. 1 shows a perspective view of a diluter/diffuser device inaccordance with an embodiment of the invention. The device comprises afirst pipe 10 that is mountable on an exhaust stack (not illustrated) ofa heavy truck. The first pipe 10 may include a reduced diameter fitting12 that can be inserted into the truck exhaust stack to facilitatemounting of the device. Heavy trucks use a standard 5 inch diameterexhaust pipe, and the invention is readily adapted to fit this standardpipe, but can be adapted to other size exhaust pipes as will beunderstood.

The first pipe 10 has an exhaust or outlet (not shown in FIG. 1; see,outlet 14 in FIG. 3) that is disposed inside a second pipe 20 ordiffuser. The second pipe 20 has a diameter greater than the diameter ofthe first pipe 10 to define an inlet gap 22 surrounding the first pipe.The inlet gap 22 allows ambient air to enter the second pipe 20 to mixwith the exhaust gas entering the second pipe from the first pipe 10.Exhaust gas and ambient air mix in the second pipe 20 as the gases flowthrough.

The diffuser 20 is made sufficiently wider than the exhaust outlet ofthe first pipe 10 so that the entering exhaust gas expands anddecelerates in the interior volume of the diffuser.

To cool the exhaust gas, the device in accordance with the inventionrelies on the buoyancy of the exhaust gas flowing through the secondpipe 20 to induce a flow of ambient air into the second pipe. Thebuoyancy or stack effect is created by the hotter exhaust gasesexpanding in the second pipe 20 and developing a pressure gradientinducing ambient air into the second pipe. Accordingly, two features ofthe invention, which will be described further below, include the secondpipe 20 being sufficiently wider than the first pipe to allow theexhaust gas exiting the first pipe to expand, and the first pipe 10 andat least a portion of the second pipe 20 being vertically oriented toallow the hot exhaust gas to entrain ambient air via buoyancy effects.

The device of the invention further includes a disperser 50 mounted atthe end of the second pipe 20, and configured to direct the mixedexhaust gas and ambient air radially outward. The disperser 50 includesan end cap or end plate 52 having a diverter 54 extending into the gasflow to direct the upward flowing gases outward. In the illustratedembodiment, the diverter 54 is a conically shaped protrusion extendingfrom a lower surface of the end plate 52.

An upper edge 24 of the second pipe 20 is flared outward and upward in afrusto-conical profile also to guide flowing gases in the radiallyoutward exiting direction of the diffuser 20.

Turning now to FIG. 2, the invention is shown in exploded view to bettershow some of the details. In FIG. 2, only an upper end portion of thefirst pipe 10 is shown, the rest being omitted for clarity of theillustration. The disperser 50 is shown removed from the second pipe 20.The end plate 52 is shown separated from the disperser 50, also forclarity.

As mentioned, the disperser 50 directs the flow of mixed exhaust gas andambient air radially outward. The end plate 52 forms a barrier at theaxial end of the diffuser and the diverter 54 is provided to help turnthe flow from the axial direction to the radial direction. An annulardeflector plate 56, which provides a second diverter, is positioned todivide the flow and direct a portion of the flow radially outward. Incombination, the end plate 52 and second diverter 56 spread or diffusethe flow over a greater outlet area than either would alone. The seconddiverter 56 is formed as a plate having a central hole 58 to allow aportion of the exhaust and air flow to flow through toward the end plate52. A lower surface 60 protrudes downward into the flow and is curved inprofile to form a guide turning the flow outward. In the illustratedembodiment, the second diverter 56 has a frusto-conical cross section.

The second diverter 56 is positioned between the upper edge 24 of thesecond pipe 20 and the end plate 52 of the disperser 50. Referring againto FIG. 1, an outlet 62 of the disperser 50 is thus defined as the areabetween the upper edge 24 of the second pipe 20 and the end plate 52 ofthe diffuser.

The disperser 50 further comprises a plurality of fins 64 which arevertically and radially oriented with respect to the axial direction ofthe device, and regularly spaced around the diffuser. The fins 64 extendradially inward from the outlet 62 of the disperser 50. The fins 64 helpdisperse and diffuse the exhaust flow over the outlet 62 area of thedisperser 50. As illustrated, the fins 64 are mounted to and support thesecond diverter 56, and form a base to support the end plate 52. Thefins 64 shown in FIG. 2 extend downward through the second pipe 20 andare mounted at their lower ends 66 to an upper end of the first pipe 10.Alternatively, the lower ends 66 of the fins 64 could be mounted to acollar (not shown), which would in turn be mounted to the upper end ofthe first pipe 10.

Alternatively, the fins 64 may be configured as shorter, extendingbetween the end plate 52 and the upper edge 24 of the second pipe 20.Brace members (not illustrated) could be provided to mount the firstpipe 10 at the inlet of the second pipe 20.

The flow characteristics of the diluter/diffuser of the invention willbe described in connection with FIG. 3, which shows a schematic view ofthe device. FIG. 3 shows the first pipe 10, an outlet 14 of the firstpipe, the second pipe 20 and the disperser 50.

As mentioned, the invention relies on two effects, diffusion of the hotexhaust gases and a buoyancy or stack effect to draw cooling ambient airinto the diffuser 20. “Stack effect” is a buoyancy induced flow that iscreated by the difference in density between a higher temperature, lowerdensity gas (in this case the exhaust gas) and a lower temperature,higher density gas (the ambient air).

The exhaust gas is allowed to expand in the second pipe 20 so as toreduce the heat flux of the gas. This spreads the thermal energy of thehot exhaust gas over a larger area (i.e., the outer surface areas of thediffuser), and decelerates the exhaust flow to a point were it caneffectively mix with ambient air.

As is known, a higher temperature, lower density gas will form a plumeas it rises through a lower temperature, higher density gas. In buoyantflow, the plume will expand at a constant 15°.

The broken lines 70 in FIG. 3 begin at the outer margin of the outlet 14of the first pipe 10 and are oriented at 15° from the vertical to showthe space a buoyant plume forming from hot exhaust gas exiting the firstpipe 10 would occupy in the second pipe 20.

Two considerations in specifying the dimensions of the second piperelative to the outlet of the first pipe are to avoid creating aVenturi-like throat at the ambient air inlet 22, and to have sufficientspace in the second pipe to allow the exhaust gas exiting the first pipeto expand to create the buoyancy effect.

The second pipe 20 is configured to be a buoyancy mixing conduit bydimensioning the second pipe to avoid constraining the plumedevelopment, so that the cross-sectional area of the exhaust plume is atleast as great as the cross-sectional area of the second pipe to inducethe ambient air flow. This relationship is illustrated by the relativeposition of the broken lines 70 indicating a plume expansion and theoutline of the second pipe in FIG. 3. Stated in terms of the diametersof the first pipe 10 and the width of the inlet gap 22, the diameter ofthe second pipe 20 is equal to or greater than the diameter of theoutlet 14 of the first pipe 10 plus twice the inlet gap 22 width.

To avoid creating a Venturi-like throat at the second pipe inlet 22, thecross-sectional area of the second pipe inlet 22 is preferablyestablished to be greater than or equal to the cross-sectional area ofthe outlet 14 of the first pipe (taking the total area surrounding thefirst pipe outlet 14). This means that the diameter of the second pipe20 is at least twice the diameter of the first pipe 10.

Taking these relationships into account, the inventor determined thatthe second pipe 20 preferably has a height (measured between the inlet22 and the upper edge 24) of at least 2.5 times the width of the inletgap 22.

As an upper limit, a height of not more than 15 times the diameter ofthe second pipe 20 is preferable. Keeping the height at not more than 15times the diameter of the second pipe 20 ensures the flow has sufficientenergy to disperse radially outward from the second pipe outlet 62.

In addition, it was determined that the outlet 62 of the disperser 50should allow for the flow of mixed gas without creating backpressure.The area of the outlet 62 is preferably greater than the area of theoutlet 14 of the first pipe 10.

The invention has been described in terms of preferred embodiments andstructure; however those skilled in the art will understand thatsubstitutions and variations may be made without departing from thescope of the invention ad defined in the appended claims.

What is claimed is:
 1. An apparatus for cooling exhaust gases from anengine exhaust, comprising: a first pipe forming a vertically directedoutlet for an exhaust conduit; a second pipe mounted to receive anexhaust gas flow from the outlet of the first pipe, the second pipehaving a diameter at least twice a diameter of the first pipe andpositioned relative to the first pipe to define an ambient air annularinlet gap surrounding the outlet of the first pipe, the second pipehaving a height that is at least 2.5 times a width of the inlet gap;and, a dispersing outlet mounted at an end of the second pipe andconfigured to direct exhaust gas radially outward, wherein thedispersing outlet comprises an end plate having a conical protrusionformed there on and directed into the exhaust flow, the plate beingspaced from an end of the second pipe to define there between a radialoutlet opening; and an unnular deflector plate mounted between the endof the second pipe and the end plate, the deflector plate having adownward facing frusto-conical protrusion wherein the annular defelctorplated has a centrally located hole sized to allow exhaust gas to passthere through.
 2. The apparatus of claim 1, wherein the second pipe hasa height that is not more than 15 times the width of the inlet gap. 3.The apparatus of claim 1, wherein an area defined by the inlet gap is atleast equal to an area of the outlet of the first pipe.
 4. The apparatusof claim 1, further comprising a plurality of vertically and radiallydisposed fins mounted to the second pipe and supporting the end plateand deflector plate.
 5. The apparatus of claim 1, wherein an areadefined by the dispersing outlet is greater than an area of the outletof the first pipe.
 6. The apparatus of claim 1, wherein the second pipehas an outwardly curving lip at an end leading to the dispersing outlet.7. An apparatus for cooling exhaust gases from an engine exhaust,comprising: a first pipe forming a vertically directed outlet for anexhaust conduit; a second pipe mounted to receive an exhaust gas flowfrom the outlet of the first pipe, the second pipe having a diameter atleast twice a diameter of the first pipe and positioned relative to thefirst pipe to define an ambient annular air inlet gap surrounding theoutlet of the first pipe, an area defined by the inlet gap is at leastequal to an area of the outlet of the first pipe, the second pipe havinga height that is at least 2.5 times a width of the inlet gap; adispersing outlet mounted at an end of the second pipe and configured todirect exhaust gas radially outward, an area defined by the dispersingoutlet being greater than an area of the outlet of the first pipe, thedispersing outlet comprising an end plate having a conical protrusionformed there on and directed into the exhaust flow, the plate beingspaced from an end of the second pipe to define therebetween a radialoutlet opening; and, an annular deflector plate mounted between the endof the second pipe and the end plate, the deflector plate having afrusto-conical cross section with a downward facing surface and acentrally located hole sized to allow exhaust gas to pass therethrough.8. The apparatus of claim 1, wherein the second pipe defines between thefirst pipe outlet and the dispersing outlet an expansion space forexhaust gas exiting the first pipe to form a buoyant plume.